Adsorption of acetic acid on ice: Experiments and molecular dynamics simulations

Abstract

Adsorption study of acetic acid on ice surfaces was performed by combining experimental and theoretical approaches. The experiments were conducted between 193 and 223 K using a coated wall flow tube coupled to a mass spectrometric detection. Under our experimental conditions, acetic acid was mainly dimerized in the gas phase. The surface coverage increases with decreasing temperature and with increasing concentrations of acetic acid dimers. The obtained experimental surface coverages were fitted according to the BET theory in order to determine the enthalpy of adsorption deltaH(ads) and the mololayer capacity N(M(dimers)) of the acetic acid dimers on ice: deltaH(ads) = (-33.5 +/- 4.2) kJ mol(-1), N(M(dimers)) = (l1.27 +/- 0.25) x 10(14) dimers cm(-2). The adsorption characteristics of acetic acid on an ideal ice I(n)(0001) surface were also studied by means of classical molecular dynamics simulations in the same temperature range. The monolayer capacity, the configurations of the molecules in their adsorption sites, and the corresponding adsorption energies have been determined for both acetic acid monomers and dimers, and compared to the corresponding data obtained from the experiments. In addition, the theoretical results show that the interaction with the ice surface could be strong enough to break the acetic acid dimers that exist in the gas phase and leads to the stabilization of acetic acid monomers on ice.

Interaction of Carboxylic Acids and Water Ice Probed by Argon Ion Induced Chemical Sputtering

“…The interaction with the ice surface could be strong enough to break the dimer form of AA; in other words, water ice can split the AA dimers. 14 Allouche and Bahr proposed the formation of stable dimers with one water molecule. 39 H 2 O molecules become attached to the pre-existing AA dimers by hydrogen bonding.…”

“…13 It is proposed that the adsorption of isolated AA dimers on ice is able to break the dimeric structure, but a near monolayer coverage of this dimer species can reform to oligomeric structures. 14 Classical molecular dynamic simulations demonstrated that AA is strongly trapped on the ice surface at 250 K. 15 Results show that partial solvation takes place, as in the case of FA, during acid adsorption at this temperature. The adsorption and incorporation processes of AA and FA are highly influenced by the formation of two hydrogen bonds between the carboxyl moiety and two water molecules.…”

“…7 By looking at the intensity of the sputtering peaks of the AA-ice system, it has been shown that solvation of AA is incomplete due to the presence of the methyl group. 20 A combined temperature-programmed desorption (TPD) and reflection absorption infrared (RAIR) spectroscopic study showed that AA condenses in its amorphous molecular form when deposited on a thin film of water ice at 100 K. 11 AA is found to adsorb on ASW and CW films initially through hydrogen bonding between CdO and dangling -OH (of ice), followed by the formation of multilayers, at 123 K. 18 The adsorption of the AA dimer on ice has been found using a coated-wall flow tube (CWFT) coupled to a mass spectrometer between the temperature window of 193 and 223 K. 14 The ability of the ice surface to induce dissociation in acids is still under debate even for the well-studied HCl-ice system. [21][22][23][24][25] Uptake of HNO 3 can lead to the formation of nitric acid hydrate.…”

“…This is the first experimental evidence for the oligomerization of AA in the presence of ice suggested by MD simulations. 14 …”

Molecular dynamics simulations of the water adsorption around malonic acid aerosol models

“…A growing number of simulation studies have thus been devoted to the characterization of the interactions between water molecules and aerosols but only a few of them have been specifically devoted to organic aerosols or organic surfaces. [2, 9-25] In contrast, such approaches have been widely used for ten years to describe the interactions between organic compounds and ice surfaces in the atmosphere, either based on ab initio calculations [26][27][28][29] or on classical simulations (Monte Carlo and molecular dynamics), [30][31][32][33][34][35][36][37][38][39][40][41][42][43] and it has been shown that these simulations led to a rather satisfactory agreement with experimental data [32-34, 38-41, 43] or in situ observations. [36] 3 While most of these studies focused on quite simple organic molecules, we recently used molecular dynamics simulations to characterize the details of the interaction between ice surfaces and more complex, difunctionalized molecules, such as hydroxyacetone [40] and oxalic acid.…”